CHICAGO, Oct 12 (Reuters) - Flooding from Hurricane Matthew has killed up to 5 million poultry birds in North Carolina, most of them chickens, the state’s top environmental official said on Wednesday, hurting a major contributor to its economy.

Donald van der Vaart, secretary of the North Carolina Department of Environmental Quality, also told Reuters that some pits that hold hog waste on farms had been inundated with floodwaters. The waste, mixing with water, may eventually make its way into rivers, streams and the Atlantic Ocean.

Van der Vaart said he did not know how many pits had been inundated but that the environmental damage would be minimal because the hog waste will be “vastly diluted” by floodwaters.

North Carolina officials have been racing to help farmers swamped by Matthew and to assess damages since the storm dumped heavy rains on the state over the weekend. They have wanted to avoid a repeat of Hurricane Floyd, which overwhelmed hog farms and pits in 1999, contaminating waterways with animal carcasses and waste.

“Knock on wood, right now we don’t have the kind of catastrophic losses we had in 1999,” van der Vaart said. He added that there had been “a tremendous loss of life on the poultry side,” however, saying the number of birds killed could total about 5 million.

Floodwaters have covered areas across central and eastern North Carolina this week, killing 19 people and forcing more than 3,800 residents to flee to shelters.

Agriculture is the state’s top industry, contributing about $84 billion to the economy, according to the North Carolina Department of Agriculture and Consumer Services.

The department has confirmed 1.8 million poultry have died, mostly chickens, spokesman Brian Long said. The total is expected to increase, he added.

Last year, North Carolina produced about 823 million chickens for meat, according to the U.S. Department of Agriculture.

Sanderson Farms Inc, the third largest U.S. poultry producer, said it lost about 250,000 chickens being raised for meat in the state.

Tyson Foods Inc said its losses were minimal because the company does did not have operations raising chickens for meat in flooded areas.

Privately held Perdue Farms said it was still assessing the number of chickens it lost.

Chicken carcasses will be disposed of primarily through composting inside the houses where the chickens were being raised, North Carolina officials said.

The state’s agriculture department said it had asked the U.S. Federal Emergency Management Agency for about $5 million to help cover composting costs.